Where I live we have very cold winds blowing in from Russia's Siberia. It is freezing despite the fact that I have all kinds of extra winter clothing like commando balaclava, SPD winter shoes, ESS goggles -- but my toes are still freezing.

ChrisW: what about with SPD shoes? do you create a hole to the plastic bags to use the cloaks?
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user652Feb 19 '11 at 15:44

@hhh If you look at the illustrations of shoe covers on the MEC web page that I linked to above, you see they have a small hole towards the front of the sole. MEC also have a whole other page of general advice about winter cycling here including the advice about feet.
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ChrisWFeb 19 '11 at 15:52

About plastic bags on their site: An inexpensive and simple solution is to put a small plastic bag over your feet or inside your shoes. Inside/outside solution, not evident in the first sight.
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user652Feb 22 '11 at 18:32

I cut both corners off a plastic shopping bag and put it over my toes inside the shoe. It's free, and barely noticeable. I wear my regular summer shoes and socks during the winter, and even on cold days when I'm walking and biking through slush and heavy snow it keeps my feet nice and warm.

Any shoes bought for winter (below freezing) cycling should be several sizes larger than a rider's normal shoe size. Stuffing more layers inside a shoe/boot that is a close fit actually makes keeping your feet warm harder since it will tend to restrict circulation. This is a very common mistake.

I normally wear a size 44, but my winter sets of shoes/boots are 45 and 50. The extra room translates to extra space for insulation (socks). If possible, you should buy winter shoes/boots in a wide size as well, so you are not just getting more room in the toe box, but throughout the shoe.

I recommend a vapor barrier sock or other method (plastic bag) to keep your insulation dry and effective.

If you have all that going on and still need more warmth, some sort or overshoe is a next step. I have found that the over booties designed for cross country skis usually work fairly well with cycling shoes and and generally relatively cheap.